Photosensitizer–Antibiotic Conjugates: A Novel Class of Antibacterial Molecules

Bacterial resistance to a variety of antibiotics has led to intensive research into the effect of photosensitizers as a cytotoxic agent against bacterial cells. In this study, we synthesized the following conjugates with or without a linker: rose bengal-penicillanic acid (RBPA), rose bengal-linker-penicillanic acid (RBLPA) and rose bengal-linker-kanamycin (RBLKAN). The antibacterial activity of these conjugates was examined on Staphylococcus aureus and Escherichia coli. Exposure of the cultures to 100 J cm⁻² showed that the minimum inhibitory concentration (MIC) of RBPA, RBLPA and RBLKAN on S. aureus was 0.195, 0.156 and 0.004 μm, respectively. The MIC of RBPA, RBLPA and RBLKAN on E. coli was 1.56, 2.5 and 0.156 μm, respectively. In dark control experiments, the MIC of these conjugates was not detected until a concentration that was 16-fold that of the MIC found in the light experiments. RBPA and RBLPA as well as RBLKAN are bactericidal for both bacterial cells. Total eradication of S. aureus and E. coli was observed with RBLKAN (0.078 and 20 μm 16 J cm⁻², respectively). Under these conditions, scanning electron microscopic analysis showed significant damage to these bacteria. However, the photosensitizer and antibiotics individually were not effective.     

Mechanism of collision-induced intersystem crossing in CO

We have studied inert-gas pressure effects on the fluorescence decay in CO selectively excited to the υ = 0 to 7 vibronic levels of the A ¹Π electronic state. It is shown that the dependence of the quenching cross section σ_isc on the average value of the ST mixing coefficient (β²) has a quasi-logarithmic form. A simple two-level model describing semiquantitatively this behavior is proposed.     

SPECTROSCOPY AND PHOTOSENSITIZATION OF SAPPHYRINS IN SOLUTIONS AND BIOLOGICAL MEMBRANES

Abstract A spectroscopic and photophysical study of three new sapphyrin molecules is presented. The sapphyrin backbone that was derivatized to make them water soluble possesses an absorption band around 700 nm, a desired property for biological photosensitization. We studied the absorption and fluorescence spectra, from which evidence for aggregation in solvents of different polarities was obtained. The extent of aggregation is correlated with the nature of the attached moiety. The absolute quantum yields of singlet oxygen production were measured, with 1,3-diphenyl isobenzofuran as a model target, and were 0.13–0.18 in ethanol. The binding constants to liposomes and to cells were determined spectroscopically and were found to correspond to the hydrophobicities of the compounds, with an additional effect, ascribed to the sugar moiety, which was found in the case of one of the sapphyrins. The efficiency of photodamage to Staphylococcus aureus by sapphyrins and hematoporphyrin was equivalent, on the basis of cells killed per microgram of sensitizer in the incubation mixture.     

Spin-boson thermal rectifier

Rectification of heat transfer in nanodevices can be realized by combining the system inherent anharmonicity with structural asymmetry. We analyze this phenomenon within the simplest anharmonic system-a spin-boson nanojunction model. We consider two variants of the model that yield, for the first time, analytical solutions: a linear separable model in which the heat reservoirs contribute additively, and a nonseparable model suitable for a stronger system-bath interaction. Both models show asymmetric (rectifying) heat conduction when the couplings to the heat reservoirs are different.     

Extreme accumulation layers on ZnO surfaces due to He+ ions

Accumulation layers with excess surface electron densities of up to 10¹⁴ cm^?2 have been produced on the (001) face of ZnO single crystals by an electrical discharge in helium atmosphere. Hall effect measurements show that at these extreme surface electron densities both the electron density and the mobility are temperature independent from room temperature down to 1.6 K.     

Spin model for inverse melting and inverse glass transition

A spin model that displays inverse melting and inverse glass transition is presented and analyzed. Strong degeneracy of the interacting states of an individual spin leads to entropic preference of the "ferromagnetic" phase, while lower energy associated with the noninteracting states yields a "paramagnetic" phase as temperature decreases. An infinite range model is solved analytically for constant paramagnetic exchange interaction, while for its random exchange analogous results based on the replica symmetric solution are presented. The qualitative features of this model are shown to resemble a large class of inverse melting phenomena. First and second order transition regimes are identified.     

Molecular wires acting as coherent quantum ratchets

The effect of laser fields on electron transport through a molecular wire weakly coupled to two leads is investigated. The molecular wire acts as a coherent quantum ratchet if the molecule is composed of periodically arranged, asymmetric chemical groups. This setup presents a quantum rectifier with a finite dc response in the absence of a static bias. The nonlinear current is evaluated in closed form within the Floquet basis of the isolated, driven wire. The current response reveals multiple current reversals together with a nonlinear dependence on the amplitude and the frequency of the laser field. The current saturates for long wires at a nonzero value, while it may change sign upon decreasing its length.